The present application expressly incorporates by reference herein the entire disclosure of U.S. application Ser. No. 09/459,891, entitled xe2x80x9cCellulose Products and Processes for Preparing the Samexe2x80x9d, which is concurrently filed with the present application.
1. Field of the Invention
The present invention is directed to water-soluble metal silicate complexes, such as water-soluble metal silicate complexes containing at least one divalent metal. The present invention is also directed to processes for preparing water-soluble metal silicate complexes. The present invention further relates to waste water treatment processes using water-soluble metal silicate complexes. The present invention also relates to processes for preparing cellulose products, such as paper products, which processes involve adding at least one water-soluble metal silicate complex to a cellulose slurry, such as a paper slurry. Similarly, the present invention relates to processes for preparing cellulose products which processes involve adding at least one water-soluble metal silicate, such as a monovalent cation silicate, to a cellulose slurry so as to form a water-soluble metal silicate complex in the cellulose slurry. The present invention is also directed to cellulose products, such as paper products, containing water-soluble metal silicate complexes.
2. Background of the Invention and Related Art
Cellulose products, such as paperboards, tissue papers, writing papers, and the like are traditionally made by producing an aqueous slurry of cellulosic wood fibers, which may contain inorganic mineral extenders or pigments. The aqueous slurry is deposited on a moving wire or fabric to facilitate the formation of a cellulose matrix. The cellulose matrix is then drained, dried, and pressed into a final cellulose product. However, during the draining step, desired solid fibers, solid fines, and other solids are often removed along with the water. In this regard, solid fines include very short pulp fibers or fiber fragments and ray cells. Solid fines also include pigments, fillers, and other nonfibrous additives that may pass through the fabric during sheet formation. Furthermore, during draining, undesired water is often retained in the cellulose matrix. The removal of the desired solids and retention of undesired water adversely affects sheet formation, and thus yields cellulose products of lower quality. Further, the loss of desired solids is wasteful and costly to cellulose product manufacturers.
As a result, the paper industry continuously strives to provide processes for papermaking that improve the paper quality, increase productivity, and reduce manufacturing costs. Chemicals are often added to the fibrous slurry before the papermaking wire or fabric to improve drainage/dewatering and retention. These chemicals are called drainage and/or retention aids. Attempts have been made to add various drainage and/or retention aids in papermaking such as silicates, silica colloidals, microgels, and bentonites.
Papermaking retention aids increase the retention of fine furnish solids during the turbulent process of draining and forming the paper web. Without adequate retention of the fine solids, they are either lost to the process effluent or accumulate to high levels in the recirculating white water loop, causing potential deposit buildup and impaired paper machine drainage. Additionally, insufficient retention of the fine solids increases the papermaker""s costs due to the loss of additives intended to be adsorbed on the fiber to provide the respective paper opacity, strength, or sizing properties.
For example, U.S. Patent No. 5,194,120 to Peats et al. discloses the addition of a cationic polymer and an amorphous metal silicate material to paper furnish to improve fines retention and drainage. The amorphous metal silicates of Peats et al. are white free-flowing powders, which form extremely small anionic colloidal particles when fully dispersed in water. These materials are usually synthesized by reacting a sodium silicate with a soluble salt of the appropriate metal ions, such as Mg2+, Ca2+, and/or Al3+, to form a precipitate which is then filtered, washed, and dried.
WO 97/17289 and family member U.S. Pat. No. 5,989,714 to Drummond relates to a method of controlling drainage and/or retention in the formation of a paper matrix by using metal silicate precipitates. The metal silicate precipitates of Drummond are prepared by mixing a soluble metal salt with a soluble silicate.
JP 63295794 A to Naka-Mura relates to a neutral or weakly alkaline papermaking process which includes adding to the pulp slurry a cationic, water-soluble polymer and an aqueous solution of sodium silicate.
JP 1072793 to Haimo discloses a method for making paper by directly adding an aqueous solution of sodium orthosilicate to the paper slurry. The orthosilicate solution of Haimo is prepared in a separate step (e.g., treatment of aluminum sulfate to adjust the pH) prior to being added to the paper slurry.
U.S. Pat. Nos. 4,927,498; 4,954,220; 5,185,206; 5,470,435; 5,543,014; 5,626,721; and 5,707,494 to Rushmere and Rushmere et al. relate to the use of polysilicate microgels as retention and drainage aids in papermaking. The microgels of many of these patents are manufactured by an on-site process by reacting polysilicic acid with an alkali metal to form microgels which are then added to a paper furnish.
U.S. Pat. No. 5,240,561 to Kaliski relates to the use of microgels in papermaking processes. The microgels of Kaliski are prepared by a two step process. The first step involves the preparation of a transient, chemically reactive subcolloidal hydrosol by blending the paper furnish with two separate solutions. The second step is to blend an aqueous solution containing at least one cross-linking agent with the furnishes resulting from the first step to cross-link the in-situ-formed chemically reactive subcolloidal hydrosol and synthesize (in-situ) the complex functional microgel cements. The resulting cements flocculate the paper furnishes to form paper sheets.
U.S. Pat. No. 4,753,710 to Langley et al. and U.S. Pat. No. 5,513,249 to Cauley are directed to the use of bentonite clays in paper making.
Despite many attempts to provide various types of drainage and retention aids, there still remains a need in the cellulose products industry to provide drainage and retentions aids that are cost effective and at the same time simple to use. In addition, there is still a need for a process of making cellulose products that yields significant improvements in retention and drainage while maintaining good formation of the cellulose product, e.g., paper sheet.
There is still a remaining need for improving retention and drainage, especially for improving drainage in large production of cellulose products where productivity is otherwise reduced due to slow water drainage through thick fibrous mats.
An object of the present invention is to provide water-soluble metal silicate complexes, such as metal silicate complexes containing at least one divalent metal.
A further object of the present invention is to improve retention and drainage control in making cellulose products, such as paper, by adding a water-soluble metal silicate complex to a cellulose slurry, such as a paper slurry, or by forming a water-soluble metal silicate complex in a cellulose slurry.
Another object of the present invention is to provide processes for preparing cellulose products which processes involve adding at least one water-soluble metal silicate complex to a cellulose slurry, such as a paper slurry.
A similar object of the present invention is to provide processes for preparing cellulose products which processes involve adding at least one monovalent cation silicate to a cellulose slurry, such as a paper slurry, so as to form water-soluble metal silicate complex in the cellulose slurry.
Still another object of the present invention is to provide cellulose products, such as paper products, containing water-soluble metal silicate complexes.
Yet another object of the present invention is to provide a process of waste water treatment comprising adding or forming a water-soluble metal silicate complex in waste water.
In accordance with one aspect, the present invention is directed to an aqueous composition, comprising a water-soluble metal silicate complex which comprises at least one divalent metal.
In accordance with another aspect, the present invention is directed to a process for preparing an aqueous composition including water-soluble metal silicate complex, comprising combining monovalent cation silicate and divalent metal ions in an aqueous environment to form the water-soluble metal silicate complex.
In accordance with still another aspect, the present invention is directed to a process of modifying cellulose slurry, comprising adding an aqueous composition having water-soluble metal silicate complex which includes divalent metal to cellulose slurry.
In accordance with yet another aspect, the present invention is directed to a process for preparing cellulose slurry, comprising adding monovalent cation silicate to cellulose slurry comprising a sufficient amount of divalent metal ions to combine with the monovalent cation silicate to form water-soluble metal silicate complex.
In accordance with another aspect, the present invention is directed to a process of making cellulose product, comprising: adding an aqueous composition having water-soluble metal silicate complex including divalent metal to cellulose slurry; and forming cellulose product from the cellulose slurry.
In accordance with yet another aspect, the present invention is directed to a process of making cellulose product, comprising: adding monovalent cation silicate to cellulose slurry comprising a sufficient amount of divalent metal ions to combine with the monovalent cation silicate to form water-soluble metal silicate complex; and forming cellulose product from the cellulose slurry.
In accordance with another aspect, the present invention is directed to a cellulose product comprising cellulose fiber and residue of at least one water-soluble metal silicate complex. Preferably, the residue is present in an amount of about 50 to 10,000 ppm, based on SiO2.
In accordance with still another aspect, the present invention is directed to a process for waste water treatment, comprising adding at least one water-soluble metal silicate complex to waste water, wherein the water-soluble metal silicate complex includes divalent metal.
In accordance with yet another aspect, the present invention is directed to a process for waste water treatment, comprising adding monovalent cation silicate to waste water, wherein the waste water comprises divalent metal ions in an amount sufficient to combine with the monovalent cation silicate to form water-soluble metal silicate complex.
In one aspect, the divalent metal comprises at least one of magnesium, calcium, zinc, copper, iron(II), manganese(II), and barium, preferably at least one of magnesium and calcium.
In another aspect, the water-soluble metal silicate complex has a SiO2 to monovalent cation oxide molar ratio of about 2 to 20, preferably about 3 to 5.
In still another aspect, the water-soluble metal silicate complex has a divalent metal to silicon molar ratio of about 0.001 to 0.25, preferably about 0.01 to 0.2.
In yet another aspect, the aqueous composition has a concentration of SiO2 of about 0.01 to 5 wt %, preferably about 0.1 to 2 wt %.
In still another aspect, the water-soluble metal silicate complex has a particle size of less than about 200 nm.
In another aspect, the water-soluble metal silicate complex comprises a water-soluble silicate in accordance with the following formula:
(1xe2x88x92y)M2O.yMxe2x80x2O.xSiO2
wherein M is monovalent cation; Mxe2x80x2 is divalent metal ion; x is from about 2 to 4; y is from about 0.005 to 0.4; and y/x is from about 0.001 to 0.25.
In one aspect, M comprises sodium, potassium, lithium, or ammonium, and preferably sodium.
In another aspect, Mxe2x80x2 comprises calcium or magnesium.
In yet another aspect, the water-soluble metal silicate complex comprises a water-soluble silicate in accordance with the following formula:
(1xe2x88x92y)Na2O.yMxe2x80x2O.xSiO2
where
Mxe2x80x2 is divalent metal ion comprising calcium or magnesium,
x is from about 2 to 4,
y is from about 0.005 to 0.4,
y/x is from about 0.001 to 0.25,
x/(1xe2x88x92y) is from about 2 to 20, and
the aqueous composition has a concentration of SiO2 of about 0.01 to 5 wt %. Preferably, y/x is from about 0.01 to 0.2, x/(1xe2x88x92y) is from about 3 to 10, and the aqueous composition has a concentration of SiO2 of about 0.1 to 2 wt %. Most preferably, y/x is from about 0.025 to 0.15, x/(1xe2x88x92y) is from about 3 to 5, and the aqueous composition has a concentration of SiO2 of about 0.25 to 1.5 wt %.
In another aspect, the monovalent cation silicate comprises at least one of sodium silicate, potassium silicate, lithium silicate, and ammonium silicate, preferably sodium silicate, such as sodium silicate having a weight ratio of SiO2/Na2O of about 2 to 4.
In another aspect, the divalent metal ions comprise at least one of magnesium and calcium.
In still another aspect, the water-soluble metal silicate complex is prepared by adding monovalent cation silicate to an aqueous reactant composition having a sufficient amount of divalent metal ions to form the water-soluble metal silicate complex.
In yet another aspect, the aqueous reactant composition having a sufficient amount of divalent metal ions has a hardness of about 1 to 600 ppm Ca equivalent. For instance, the aqueous reactant composition may comprise at least one of tray water, hard water, and treated water which treated water is prepared by increasing or decreasing hardness.
In another aspect, a source of the divalent metal ions comprises at least one of CaCl2, MgCl2, MgSO4, Ca(NO3)2, Mg(NO3)2, CaSO4, and ZnSO4.
In yet another aspect, the water-soluble metal silicate complex is prepared by adding divalent metal ions to an aqueous reactant composition having a sufficient amount of monovalent cation silicate to form the water-soluble metal silicate complex.
In one aspect, the aqueous reactant composition having a sufficient amount of monovalent cation silicate has a concentration of SiO2 of about 0.01 to 30 wt %.
In another aspect, the water-soluble metal silicate complex is added to cellulose slurry after a last high shear stage and before a headbox.
In yet another aspect, at least one additive comprising one of flocculent, starch, and coagulant, is added to the cellulose slurry. For instance, the at least one additive may be cationic polyacrylamide copolymer. The at least one additive may be added to the cellulose slurry at a point before a last high shear stage.
In another aspect, the water-soluble metal silicate complex comprises a water-soluble silicate in accordance with the following formula:
(1xe2x88x92y)Na2O.yMxe2x80x2O.xSiO2
where
Mxe2x80x2 is divalent metal ion comprising calcium or magnesium,
x is from about 2 to 4,
y is from about 0.005 to 0.4,
y/x is from about 0.001 to 0.25,
x/(1xe2x88x92y) is from about 2 to 20,
the aqueous composition has a concentration of SiO2 of about 0.01 to 5 wt %, and at least one of flocculent, starch, and coagulant is added to the cellulose slurry.
The particulars shown herein are by way of example and for purposes of illustrative discussion of the various embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
All percent measurements in this application, unless otherwise stated, are measured by weight based upon 100% of a given sample weight. Thus, for example, 30% represents 30 weight parts out of every 100 weight parts of the sample.
Unless otherwise stated, a reference to a compound or component, includes the compound or component by itself, as well as in combination with other compounds or components, such as mixtures of compounds.
Before further discussion, the following terms will be discussed to aid in the understanding of the present invention.
xe2x80x9cHardnessxe2x80x9d refers to the total concentration of divalent metal ions or their salts in water, e.g., calcium, magnesium, calcium carbonate, and calcium chloride. Hardness may be measured in parts per million of Ca equivalents. In this regard, 1 ppm Ca equivalent is equal to 2.78 ppm CaCl2 equivalent which is equal to 2.50 ppm CaCO3 equivalent and which is equal to 0.61 ppm Mg equivalent.
xe2x80x9cWater-solublexe2x80x9d and xe2x80x9cstabilityxe2x80x9d refer to the ability of the metal silicate complexes of the present invention to remain in solution. When the water-soluble metal silicate complexes of the present invention are formed, the process may be controlled so that no precipitate is formed. However, under some circumstances, a slight amount of precipitate may form. If the metal silicate complexes form precipitate, they are no longer complexes, but are metal silicate precipitate. In the present invention, it is desired that the metal silicate complexes of the present invention remain in solution and do not form a precipitate. It is noted that some of the water-soluble metal silicate complex may precipitate with time, however, it is preferred that no precipitate or a minimal amount of precipitate is formed. As long as the metal silicate complexes are water-soluble, the solutions should be essentially colorless and clear. In this regard, the water-soluble metal silicate complexes of the present invention are not visible to the naked eye. In particular, considering that turbidity depends on concentration, an aqueous composition of the water-soluble metal silicate complex of the present invention having a concentration of 0.3 wt % of SiO2, in the absence of other materials that affect turbidity, would preferably have a turbidity of less than about 70 NTU, more preferably less than about 50 NTU, and most preferably less than about 20 NTU. The water-soluble metal silicate complexes of the present invention cannot be separated from the aqueous phase by most physical or mechanical separation techniques, such as centrifugation, sedimentation, or filtration.
xe2x80x9cCellulose slurryxe2x80x9d refers to a water-based slurry containing cellulose fibers and fines, and which may contain other additives.
xe2x80x9cPaper slurryxe2x80x9d or xe2x80x9cpaper furnishxe2x80x9d refers to a water-based slurry containing cellulose fibers and/or fines, such as of wood, vegetable, and/or cotton, and which may contain other additives for papermaking such as fillers, e.g., clay and precipitated calcium carbonate.
xe2x80x9cCopolymerxe2x80x9d refers to a polymer comprising two or more different kinds of monomers.
As an overview, the present invention relates to water-soluble metal silicate complexes, such as metal silicate complexes containing at least one divalent metal. The present invention is also directed to processes for preparing water-soluble metal silicate complexes. The present invention further relates to waster water treatment processes using water-soluble metal silicate complexes. The present invention also relates to processes for making cellulose products, such as paper products, by adding at least one water-soluble metal silicate complex to a cellulose slurry, such as a paper slurry. Similarly, the present invention relates to processes for making cellulose products by adding at least one monovalent cation silicate to a cellulose slurry so as to form a water-soluble metal silicate complex in the cellulose slurry. By adding or forming a water-soluble metal silicate complex in a cellulose slurry, the present invention is capable of improving retention and drainage control in making cellulose products. The present invention is further directed to cellulose products, such as paper products, containing water-soluble metal silicate complexes.
The water-soluble metal silicate complexes of the present invention preferably contain at least one kind of divalent metal ion and at least one kind of monovalent cation.
Examples of divalent metal ions useful in the water-soluble metal silicate complexes of the present invention include, but are not limited to, ions of alkaline earth metals and transition metals. In particular, the divalent metal ions may include magnesium, calcium, zinc, copper, iron(II), manganese(II), and/or barium. Preferably, the divalent metal ions include magnesium, calcium, and/or zinc. Most preferably, the divalent metal ions include magnesium and/or calcium.
Examples of monovalent cations useful in the water-soluble metal silicate complexes of the present invention include, but are not limited to, ions of alkaline metals. In particular, the monovalent cations may be sodium, potassium, lithium, and/or ammonium. Preferably, the monovalent cations are sodium and/or potassium. Most preferably, the monovalent cations are sodium.
In a preferred embodiment of the present invention, the metal silicate complex is a magnesium silicate complex and/or a calcium silicate complex prepared by adding sodium silicate to an aqueous composition containing magnesium and/or calcium ions. Preferably, an aqueous composition of the water-soluble metal silicate complex of the present invention comprises SiO2 in an amount of about 0.01 to 5 wt % by weight of the aqueous composition, has a SiO2/monovalent cation oxide, such as Na2O, molar ratio from about 2 to 20, and a [(divalent metal, e.g., Mg+Ca)/Si] molar ratio from about 0.001 to 0.25.
Not wishing to be bound by theory, the water-soluble metal silicate complexes of the present invention are believed to include water-soluble metal silicate complexes having the following formula:
(1xe2x88x92y)M2O.yMxe2x80x2O.xSiO2xe2x80x83xe2x80x83formula (1)
where:
M is a monovalent cation, such as those discussed above,
Mxe2x80x2 is a divalent metal ion, such as the divalent metal ions discussed above,
x is preferably from about 2 to 4,
y is preferably from about 0.005 to 0.4, and
y/x is preferably from about 0.001 to 0.25.
The ability of the metal silicate complexes of the present invention to remain in solution, i.e., the stability of the metal silicate complexes, is important to achieving the results of the present invention. For instance, stability is important with respect to improving retention and drainage control in cellulose products making. In particular, the metal silicate precipitates which may be formed have low or no activity with respect to retention and drainage control. In some cases, the metal silicate complexes have a slight precipitate and still demonstrate reasonable retention and drainage activity, because an insignificant portion of the metal silicate complexes are converted to precipitate and the majority of the components remain water-soluble. As discussed above, an aqueous composition of the water-solubility complex of the present invention having SiO2 at a concentration of 0.3 wt %, in the absence of other materials that affect turbidity, would preferably have a turbidity of less than about 70 NTU, more preferably less than about 50 NTU, and most preferably less than about 20 NTU.
The ability of the metal silicate complexes of the present invention to remain in solution, i.e., stability, generally depends upon several factors. These factors include molar ratio of SiO2/M2O, molar ratio of Mxe2x80x2/Si, concentration of SiO2, size of the microparticles of the complex, hardness of the aqueous composition in which the complexes are formed, agitation applied during formation of the metal silicate complexes, pH of the aqueous composition, temperature of the aqueous composition, and solutes in the aqueous composition. Of these factors, the most important are molar ratio of SiO2/M2O and molar ratio of Mxe2x80x2/Si. The ability of the metal silicate complexes to remain in solution depends upon an interaction of these factors, as discussed in more detail below.
Before discussing variables affecting the stability of the water-soluble metal silicate complexes involved in the process of making the water-soluble metal silicate complexes, a discussion of stability factors which are specific to the complexes themselves is as follows. The factors affecting the stability of the metal silicate complexes which are specific to the metal silicate complexes per se of the present invention include molar ratio of SiO2/M2O, molar ratio of Mxe2x80x2/Si, and size of the microparticles forming the complexes.
The water-soluble metal silicate complexes of the present invention preferably have an SiO2/M2O molar ratio, i.e., x:(1xe2x88x92y) for compounds in accordance with formula (1), in the range from about 2 to 20, more preferably from about 3 to 10, and most preferably from about 3 to 5. When this value is too high, the metal silicate complex could form a precipitate and lose activity. When this value is too low, a relatively small amount of metal silicate complex is formed.
The water-soluble metal silicate complexes of the present invention preferably have an Mxe2x80x2/Si molar ratio, i.e., y:x for compounds in accordance with formula (1), in the range from about 0.001 to 0.25, preferably from about 0.01 to 0.2 , and more preferably 0.025 to 0.15. When this value is too high, the metal silicate complex could form a precipitate and lose activity. When this value is too low, a relatively small amount of metal silicate complex is formed.
It is expected that the water-soluble metal silicate complexes of the present invention have a microparticle size preferably less than about 200 nm, with a range of preferably about 2 to 100 nm, and more preferably about 5 to 80 nm, as measured by dynamic light scattering at 25xc2x0 C. in aqueous solution. It is believed that if the particle size is too large, the metal silicate complexes will form precipitate. If the particle size is too small, the metal silicate complexes will not have enough flocculating power.
Before discussing variables of making the metal silicate complexes which affect the stability of the water-soluble metal silicate complexes of the present invention, an overview of the process of making the water-soluble metal silicate complexes of the present invention is presented.
The water-soluble metal silicate complexes of the present invention can be prepared by adding at least one monovalent cation silicate to an aqueous composition containing divalent metal ions. When at least one monovalent cation silicate is mixed with an aqueous composition containing divalent metal ions, the water-soluble metal silicate complexes are spontaneously formed during mixing of the monovalent cation silicates and the aqueous composition. The water-soluble metal silicate complexes of the present invention may also be prepared by providing an aqueous composition comprising at least one monovalent cation silicate and simultaneously and/or subsequently adding a source of divalent metal ions to form the water-soluble metal silicate complex of the present invention. The water-soluble metal silicate complexes of the present invention can be formed as a concentrate in an off-site factory or may be prepared on-site, e.g., at a paper mill.
The monovalent cation silicates which are used to form the water-soluble metal silicate complexes of the present invention can be in the form of a powder or a liquid. Examples of the monovalent cation silicates which are used to form the water-soluble metal silicate complexes include silicates of alkaline metals. Particularly preferred examples of silicates for making the water-soluble metal silicate complexes of the present invention include sodium silicate, potassium silicate, lithium silicate, and/or ammonium silicate.
As discussed above, examples of divalent metal ions useful in making the water-soluble metal silicate complexes of the present invention include, but are not limited to, alkaline earth metals and transition metals. In particular, the divalent metal ions may be magnesium, calcium, zinc, copper, iron(II), manganese(II), and/or barium.
Examples of aqueous compositions having divalent metal ions include, but are not limited to, tray water, hard water, treated water, and cellulose slurry. xe2x80x9cTray waterxe2x80x9d which is also known as xe2x80x9csilo waterxe2x80x9d refers to water collected from a cellulose product machine during cellulose product making, e.g., water collected from a paper machine during and after papermaking. xe2x80x9cHard waterxe2x80x9d refers to water containing a substantial amount of metal ions, such as Mg2+ and/or Ca2+ ions. xe2x80x9cTreated waterxe2x80x9d refers to hard or soft water which has been treated to increase or decrease hardness. If the water hardness is too high, as discussed below, some of the metal ions may be blocked or deactivated by any known manner, such as by adding chelating agent, e.g., ethylenediaminetetraacetic acid (EDTA), hydroxyethylethlenediaminetriacetic acid (HEDTA), tartaric acid, citric acid, gluconic acid, polyacrylic acid. If the water hardness is too low, as discussed below, divalent metal ions may be added. For instance, magnesium and/or calcium salt can be added to increase metal ions, and thus increase water hardness. In particular, CaCl2, MgCl2, MgSO4, Ca(NO3)2, Mg(NO3)2, CaSO4, and/or ZnSO4, preferably CaCl2, MgCl2, and/or ZnSO4, more preferably CaCl2 and/or MgCl2, can be added to the aqueous composition to increase the concentration of metal ions.
With the above in mind, several variables of the process of making the water-soluble complexes affect the ability of the metal silicate complexes to remain in solution. These process variables include concentration of SiO2 in the aqueous composition, hardness of the aqueous composition, agitation applied during formation of the water-soluble metal silicate complexes, pH of the aqueous composition, temperature of the aqueous composition, and additional solutes in the aqueous composition. Of these variables, the concentration of SiO2 in the aqueous composition and the hardness of the aqueous composition are the most important.
When a monovalent cation silicate is combined with a divalent metal ion to form an aqueous composition comprising the water-soluble metal silicate complexes of the present invention, the resulting aqueous composition preferably has a concentration of SiO2 of about 0.01 to 5 wt %, more preferably from about 0.1 to 2 wt %, and most preferably from about 0.25 to 1.5 wt %, by weight of the aqueous composition. When this value is too high, the metal silicate complex could form a precipitate and lose activity. When this value is too low, the solution is not economical because a large amount of solution is required.
When divalent metal ions are added to an aqueous composition comprising monovalent cation silicate, the aqueous composition preferably has a concentration of SiO2 of about 0.01 to 30 wt %, more preferably from about 0.1 to 15 wt %, and most preferably from about 0.25 to 10 wt %, by weight of the aqueous composition. When this value is too high, the metal silicate complex could form a precipitate and lose activity. When this value is too low, the composition is not economical because a large amount of the aqueous composition is required.
When monovalent cation silicate is added to an aqueous composition having divalent metal ions, the aqueous composition of the present invention preferably has a hardness from about 1 to 600 ppm Ca equivalent, more preferably from about 10 to 200 ppm Ca equivalent, and most preferably from about 20 to 100 ppm Ca equivalent. If the hardness is too high, the metal silicate complex may precipitate. If the hardness is too low, the water-soluble metal silicate complex may not form.
Agitation applied during formation of the metal silicate complexes also affects the ability of the metal silicate complexes to remain in solution. If no agitation is applied, under some circumstances, the water-soluble complex of the present invention may locally precipitate due to overconcentration. The effect of agitation, however, is difficult to quantify. The amount of agitation depends upon such factors as the amount and viscosity of the solution, size of the container, size and type of stirrer bar or propeller, rotation speed of stirrer or mixer, and so on. For example, in laboratory preparation, when a 100 ml of a metal silicate complex solution in a 200 ml beaker is mixed using a 1xe2x80x3 stirrer bar on a MIRAK(trademark) Magnetic Stirrer (Model #L SOand3235-60, Bernstead Thermolyne Corporation, 2555 Kerper Blvd., Dubuque, Iowa 52004), 300 rpm or higher mixing speed should be proper. In general, as long as possible, agitation should be maximized. However, if agitation is too high, it may not be economical due to overconsumption of energy, or it may cause vibration of the equipment or split of the solution.
Although the pH of the aqueous composition is expected to be an important factor in the ability of the metal silicate complexes to remain in solution, the precise effect of the pH has not been studied. However, the present invention has been found to work with tray to water as an example. Tray water typically has a pH from about 6 to 10, more typically from about 7 to 9, and most typically from about 7.5 to 8.5.
The temperature of the aqueous composition is preferably about 5 to 95xc2x0 C., more preferably about 10 to 80xc2x0 C., and most preferably about 20 to 60xc2x0 C. For instance, tray water in the paper machine is typically warm and typically has a temperature from about 10 to 60xc2x0 C., more typically from about 30 to 60xc2x0 C., and most typically from about 45 to 55xc2x0 C. Thus, the metal silicate complexes may be formed at ambient temperature. At lower Mxe2x80x2/Si ratio, increasing the temperature will accelerate the formation of the metal silicate complexes. At higher Mxe2x80x2/Si ratio, the temperature has little effect.
Another factor which is expected to affect the ability of the metal silicate complexes to remain in solution is the presence of solutes in the aqueous composition. In other words, it is expected that the presence of counterions would affect the stability of the metal silicate complexes.
The present invention is also directed to processes for preparing cellulose slurries, such as paper slurries, and to processes of making cellulose products, such as paper. In particular, the above-noted water-soluble metal silicate complexes of the present invention may be added to a cellulose slurry. Further, the processes for preparing cellulose slurries and products of the present invention may involve adding at least one of the above-noted monovalent cation silicates to a cellulose slurry containing at least one kind of the above-noted divalent metal ions.
The cellulose slurries of the present invention may contain fillers, such as those known in the art, such as clay, titanium dioxide, ground calcium carbonate, or precipitated calcium carbonate. The pH and temperature of the cellulose slurry are not considered to be important factors in the present invention. As long as the pH and temperature of the cellulose slurry are under normal conditions, such as pH in a range of about 4 to 10 and temperature of about 5 to 80xc2x0 C., the water-soluble metal silicate complexes of the present invention are expected to be effective.
When a monovalent cation silicate is added to the cellulose slurry to form a water-soluble metal silicate complex in situ, the cellulose slurry of the present invention preferably has a hardness from about 1 to 600 ppm (part per million) Ca equivalent, more preferably from about 10 to 200 ppm Ca equivalent, and most preferably from about 20 to 100 ppm Ca equivalent. If the cellulose slurry has a hardness from about 1 to 600 ppm Ca equivalent, the monovalent cation silicate can react with the divalent metal ions in the cellulose slurry and form the water-soluble metal silicate complex of the present invention.
The monovalent cation silicate or water-soluble metal silicate complex of the present invention is preferably added to the cellulose slurry at a point after the last high shear stage, but before the headbox, to avoid having the flocs formed subjected to excessive shear forces.
According to the present invention, the water-soluble metal silicate complex or the monovalent cation silicate is preferably added at a dosage from about 0.1 to 20 lb/ton, more preferably from about 0.5 to 6 lb/ton, most preferably about 1 to 4 lb/ton, based on SiO2 and the dry weight of the cellulose slurry.
In addition, at least one additive can be added to the cellulose slurry in conjunction with the water-soluble metal silicate complex of the present invention. For example, the at least one additive may include substantially any additive which is used for papermaking. Examples of the additives include, but are not limited to, flocculant, cationic starch, coagulant, sizing agent, wet strength agent, dry strength agent, and other retention aids.
The order of addition of the at least one additive and water-soluble silicate, i.e., the water-soluble metal silicate complex and/or the monovalent cation silicate, to the cellulose slurry is not critical. However, the water-soluble silicate is preferably added to the cellulose slurry after addition of the at least one additive. For instance, the water-soluble silicate may be added to the cellulose slurry after addition of flocculent. Preferably, flocculent is added at a point before the last high shear stage, such as the pressure screen and cleaners, while the water-soluble silicate is added after the last high shear stage, but prior to the headbox.
When two or more additives are added to the cellulose slurry of the present invention, the preferred additives include flocculant and starch. The starch can be added to the cellulose slurry before or after the flocculent. Preferably, the starch is added before the flocculent.
When coagulant is added to the cellulose slurry in conjunction with a flocculant and/or starch, it can be added before or after the flocculant and/or starch.
According to the present invention, the flocculant can be either a synthetic or natural polymer that is cationic, anionic, or substantially nonionic. Preferably, the flocculent is cationic.
Examples of cationic flocculants include, but are not limited to, homopolymers or copolymers containing at least one cationic monomer selected from the following: dimethylaminoethylmethacrylate (DMAEM), dimethylaminoethylacrylate (DMAEA), methacryloyloxyethyltrimethylammonium chloride (METAC), dimethylaminopropylmethacrylate(DMAPMA),methacrylamidopropyl-trimethylammonium chloride (MAPTAC), dimethylaminopropylacrylamide (DMAPAA), acryloyloxyethyltrimethylammonium chloride (AETAC), dimethaminoethylstyrene, (p-vinylbenzyl)-trimethylammonium chloride, 2-vinylpyridine, 4-vinylpyridine, vinylamine, and the like. For example, the cationic flocculent may be a cationic polyacrylamide copolymer.
The molecular weight of the cationic flocculant is preferably from at least about 500,000, with a range of preferably about 2,000,000 to 15,000,000, more preferably about 4,000,000 to 12,000,000, and most preferably about 5,000,000 to 10,000,000.
The degree of cationic substitution for the cationic flocculant is preferably at least about 1 mol %, with a range of preferably about 5 to 50 mol %, even more preferably from about 10 to 30 mol %.
The potential charge densities for the cationic flocculant is preferably 0.1 to 4 meq/g, more preferably from about 0.5 to 3 meq/g, and most preferably about 1 meq/g to 2.5 meq/g.
In the cellulose product making process of the present invention, the dosage of the cationic flocculant is preferably about 0.1 to 4 lb/ton, more preferably about 0.2 to 2 lb/ton, and most preferably about 0.25 to 1 lb/ton, based on active ingredient of the flocculent and dry weight of the cellulose slurry.
Suitable anionic flocculants of the present invention can be homopolymers or copolymers containing anionic monomers selected from the following: acrylate, methacrylate, maleate, itaconate, sulfonate, phosphonate, and the like. For example, the anionic flocculant may be poly (acrylamide-co-acrylate).
The molecular weight of the anionic flocculants of the present invention is preferably at least about 500,000, with a range of preferably about 5,000,000 to 20,000,000, and more preferably from about 8,000,000 to 15,000,000.
The degree of anionic substitution for the anionic flocculant is preferably at least about 1 mol %, with a range of preferably about 10 to 60 mol %, more preferably about 15 to 50 mol %.
The potential charge densities for the anionic flocculant is preferably about 1 to 20 meq/g, more preferably about 2 to 8 meq/g, and most preferably about 2.5 to 6 meq/g.
In the cellulose product making process of the present invention, the dosage of the anionic flocculant is preferably about 0.1 to 4 lb/ton, more preferably about 0.2 to 2 lb/ton, and most preferably about 0.25 to 1 lb/ton, based on active ingredient of the flocculant and dry weight of the cellulose slurry.
Examples of the substantially nonionic flocculants of the present invention include, but are not limited to, polyacrylamide, poly(ethylene oxide), polyvinylalcohol, and poly(vinylpyrrolidinone), preferably polyacrylamide, poly(ethylene oxide), and polyvinylalcohol, and more preferably polyacrylamide and poly(ethylene oxide).
The molecular weight of the substantially nonionic flocculant is preferably at least about 500,000, with a range of preferably about 1,000,000 to 10,000,000, more preferably from about 2,000,000 to 8,000,000.
In the cellulose product making process of the present invention, the dosage of the substantially nonionic flocculant is preferably about 0.2 to 4 lb/ton, more preferably about 0.5 to 2 lb/ton, based on active ingredient of the flocculant and dry weight of the cellulose slurry.
As discussed above, cationic starch, including amphoteric starch, may also be added to the cellulose slurry of the present invention. Preferably, cationic starch is used in cellulose product making as a wet or dry strength additive. The cationic starch of the present invention preferably has a cationic charge substitution of at least about 0.01, with a range of preferably about 0.01 to 1, more preferably about 0.1 to 0.5. The cationic starch can be derived from a variety of plants, such as potato, corn, waxy maize, wheat, and rice.
The molecular weight of the starch is preferably about 1,000,000 to 5,000,000, more preferably about 1,500,000 to 4,000,000, and most preferably about 2,000,000 to 3,000,000.
The starch of the present invention can be added to the cellulose slurry at a point before or after the flocculant, preferably before the water-soluble silicate of the present invention. The preferred dosage for the starch is from about 1 to 50 lb/ton, more preferably from about 5 to 20 lb/ton, based on dry weight of the cellulose slurry.
Another additive that can be added to the cellulose slurry of the present invention is coagulant. Examples of coagulants of the present invention include, but are not limited to, inorganic coagulants, such as alum, or similar materials, such as aluminum chloride, polyaluminum chloride (PAC), polyaluminum sulfate (PAS), and polyaluminum sulfate silicate (PASS), or organic coagulants such as polyamines, poly(diallyl dimethyl ammonium chloride), polyethyleneimine, polyvinylamine, and the like, preferably the inorganic coagulants, and more preferably alum, or similar materials.
The molecular weight of the organic coagulant is preferably about 1000 to 1,000,000, more preferably about 2000 to 750,000, more preferably from about 5000 to 500,000.
The coagulant of the present invention can be added to the cellulose slurry at a point before or after the flocculent, preferably before the water-soluble silicate. The preferred dosage for the inorganic coagulant is from about 1 to 30 lb/ton, more preferably from about 5 to 20 lb/ton, based on dry weight of the cellulose slurry. The preferred dosage for the organic coagulant is 0.1 to 5 lb/ton, more preferably about 0.5 to 2 lb/ton.
The cellulose slurry of the present invention may be formed into cellulose products through any method. For example, after the addition or formation of the water-soluble metal silicate complex, and optionally the addition of at least one additive to a cellulose slurry, the cellulose slurry may be deposited on a papermaking wire, drained, dried, and pressed into a final cellulose product.
The resulting cellulose product comprises cellulose fiber and residue of at least one water-soluble metal silicate complex. Preferably, the amount of the residue in the cellulose product is about 50 to 10,000 ppm, more preferably about 250 to 3000, and most preferably about 500 to 2000 ppm, based on SiO2.
Since retention and drainage aids typically finction as flocculating agents which are also useful in treating waste water, it is expected that the water-soluble metal silicate complexes of the present invention would also be used to treat waste water. To treat waste water, the water-soluble metal silicate complex would be added to the waste water to cause suspended particles to precipitate.
The water-soluble metal silicate complexes and processes of the present invention result in several advantages. In particular, the water-soluble metal silicate complexes and processes of the present invention yield significant improvements in retention and drainage while maintaining good formation of the cellulose sheet. The use of the complexes of the present invention as a drainage aid is beneficial in cellulose products making, especially when a large amount of drainage is required (e.g., at least about 76 lb/3300 sq. ft) where productivity would otherwise be reduced due to slow water drainage through relatively thick fibrous mats.
Thus, the water-soluble metal silicate complexes and processes of the present invention can be used to increase production rates. In this regard, the dewatering or drainage of the fibrous slurry on the wire or screen is often the limiting step in achieving higher product rates.
Increased dewatering can also result in a dryer cellulose sheet in the press and dryer sections, and thus can reduce steam consumption. The dryer section is also the stage in a cellulose products making process that determines many final sheet properties.
Similarly, when used as retention aids, the metal silicates of the present invention reduce the loss of fillers and fines, and thus reduce production costs. In addition, complexes of the present invention also provide excellent paper formation due to proper drainage and retention.
Further, the process of preparing the water-soluble metal silicate complexes of the present invention is simple and does not require any special manufacturing process.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its flillest extent. The present invention will be further illustrated by way of the following Examples. These examples are non-limiting and do not restrict the scope of the invention.